Lecture 13: Practical Design, The Future of Prestressed Concrete, and Concluding Thoughts...

Transcription

1 Lecture 13: Practical Design, The Future of Prestressed Concrete, and Concluding Thoughts... LECTURE 13 May 17, 2005 May 17,

2 Where we have been Basics Allowable Stress Ultimate Strength Shear Camber Basic Bridge Design Continuous Spans May 17,

3 Final Exam 2 Hours Tuesday May 24 th 7pm -9pm Not Cumulative in respect to calculations, but understand concepts Covers: Lectures 6 12 (shear to continuous beams) Open Book, Open Notes Questions? May 17,

4 Totally Precast Concrete Bridges May 17,

5 Is it possible to design an Instant Bridge? Almost! There are many ways to put a bridge together quickly with precast concrete products. May 17,

6 The speed and variety of precast prestressed products and methods give designers many options. Consider these advantages of an all-precast bridge May 17,

7 Benefits to Owner Agencies: Reduction in the duration of work zones Reduced traffic handling costs Reduced accident exposure risks Less inconvenience to the traveling public Fewer motorist complaints Fast construction benefits owner agencies by reducing the duration of the work zone. Fast construction reduces traffic handling costs and accident exposure risks. There s less inconvenience to the traveling public, fewer delays, and fewer motorist complaints. According to a report by the Texas Transportation Institute, costs incurred by drivers passing through a work zone (along with engineering costs) can be $10,000 to $20,000 per day. A recent Federal report indicates user costs of $50,000 per day for work zones in urban areas. May 17,

8 Benefits to Contractors: Reduced exposure to hazards More work -- less time Fewer weather delays Lower costs Less skilled labor Contractors benefit from reduced exposure to traffic hazards. More work can be accomplished in less time, with fewer weather delays. Costs are lower for forms, skilled field labor, scaffolding and shoring, and cranes. May 17,

9 After foundations have been completed, scheduling can be controlled by a single contractor working with a familiar material. Scheduling Control May 17,

10 Precast concrete structural elements should always be plant produced under carefully controlled conditions by plants that are Certified by PCI. Plant-produced Elements May 17,

11 so all structural elements benefit from the excellent quality and corrosion resistance of prestressed concrete. Quality and Corrosion Resistance May 17,

12 Fully-cured precast concrete structural elements can be stockpiled in advance of need Stockpiled in Advance May 17,

13 and can be scheduled for justin-time delivery and erection Immediate Delivery and Erection May 17,

14 There s no curing time required at the jobsite, as with castin-place concrete. Bridge piers can be erected in a day, and beams can follow immediately. No Curing Time May 17,

15 The following photos illustrate the many products and construction methods that enable very rapid project completion. In addition to the often-used superstructure elements of girders and deck slabs, substructure components such as these piers can also be precast. May 17,

16 Precast concrete piles are quite popular in much of the country. They come in different sizes and shapes, ranging from 10-inch square piles to 66- inch diameter hollow cylinder piles. May 17,

17 Pile caps also can be precast concrete, reducing exposure, forming and curing in the field. May 17,

18 Piers can be made of precast concrete pieces quickly assembled in the field. May 17,

19 Abutments can also be made of precast. May 17,

20 The Sucker Creek Bridge in Hague, New York, consists of precast concrete box beams supported on precast concrete abutments assembled into a jointless, rigid frame. Sucker Creek Bridge in Hague May 17,

21 In San Juan, Puerto Rico, the totally precast concrete Baldorioty de Castro Avenue bridges were built in record-setting time, attractively, and economically. Puerto Rico May 17,

22 Puerto Rico - A totally precast bridge Each of four bridges, ranging in length from 700 to 900 feet, was erected in about 24 hours. This was well within the owner s construction allowance of 72 hours per bridge, a condition established to minimize disruption to one of the city s highly traveled corridors. May 17,

23 In addition to speed, the bridges also met the city s budgetary needs. The four box-beam bridges were constructed for $2 million less than the next lowest bid for another material. Puerto Rico May 17,

24 Confederation Bridge New Brunswick, Canada Totally precast bridge systems may be the only viable solution in harsh field conditions. The Confederation Bridge connecting Canada s Prince Edward Island to mainland New Brunswick is such an example. The bridge spanned the eight-mile-wide Northumberland strait, which experiences severe winters and is covered with ice floes for five months of the year. May 17,

25 Even in such harsh conditions, precast concrete was able to meet the owner s requirements of a 100-year service life, a 3½-year construction period, and attractiveness. Confederation Bridge May 17,

26 Edison Bridge Florida It just makes economic sense to evaluate conversion of cast-in-place to precast concrete. This was done for the Edison Bridge in Florida. Precast piers and beams were spliced to produce tall pier bents. May 17,

27 Texas - Precast Piers The state of Texas has constructed several bridges with segmental precast concrete piers. The attractive piers and pier caps are hollow members. Some are made of highperformance concrete. Such segments may be match-cast, similar to segmental box girder bridges, or separated by a thin mortar bed, much like giant masonry units. May 17,

28 In Houston, the Louetta Road Overpass utilized precast concrete match-cast piers, as well as precast, prestressed U-beams and stay-in-place deck panels. Louetta Road Bridge Texas May 17,

29 Sunshine Skyway Bridge Florida Another famous bridge is the Sunshine Skyway Bridge over Tampa Bay in Florida. The piles, piers and pier caps were constructed of precast concrete elements connected together with posttensioning threadbars. May 17,

30 Making Bridges L o n g e r... Why? Spans greater that 165 ft are generally not economical Transportation problems Lifting restrictions Result? Owners and designers go with steel alternative. Good for the steel industry Bad for the prestressed industry! May 17,

31 Making Bridges L o n g e r... Solutions? New high strength materials New beam shapes Continuity Splices May 17,

32 Making Bridges L o n g e r... Wider bottom flanges mean more strands in the right places NU I-girders Washington Super Girders New England Bulb-Tee May 17,

33 Making Bridges L o n g e r... May 17,

34 Making Bridges L o n g e r... Use of 0.6 diameter strands. Same center-to-center spacing as 0.5 diameter! 40% more pretension force with only a 20% increase in diameter! May 17,

35 Continuity Make simple spans continuous over the piers by: Deck Reinforcement Post-Tensioning Coupling beams with high strength rods Coupling beams with prestressing strands May 17,

36 Continuity: Deck Reinforcement Method discussed previously Simple span for dead load, continuous for live loads. The reinforcement in the deck resists the negative moment from the continuous live loads. Simplest Method May 17,

37 Continuity: Post-Tensioning More expensive generally Very efficient Pre-compression of the deck in the negative moment region reduces deck cracking at the piers Post-tensioning resists some of the beam self-weight and deck. May 17,

38 Continuity: Post-Tensioning May 17,

39 Continuity: Coupled High-Strength Rods Similar to Deck reinforcement method Threaded rods (non-prestressed) in the top flanges regions resist negative moment Provides continuity for deck weight, super-imposed dead loads and live loads. May 17,

40 Continuity: Coupled High-Strength Rods May 17,

41 Continuity: Coupled High-Strength Rods May 17,

42 Continuity: Coupled Prestressing Strands Utilizes prestensioned strands that are left extended at the ends of beams. Before placing the deck, the strands are spliced and tensioned. Procedure is complex and new, but results show promise and may reduce costs associated with post tensioning. May 17,

43 Splices Utilizes prestressing and posttensioning to provide much longer spans. May be competitive to steel options. Especially as the price of steel continues to rise... May 17,

44 Splices May 17,

45 Splices: Cast-in-Place Post- Tensioned Splice May 17,

46 Splices: Cast-in-Place Post- Tensioned Splice May 17,

47 Splices: Cast-in-Place Post- Tensioned Splice May 17,